The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of common general knowledge in the field.
HMF (hydroxymethyl furfural) is considered as a key platform molecule in the transformation of biomass into chemicals. However, HMF that can be derived from sugars, such as fructose or glucose, is not stable and is difficult to isolate easily. On the contrary, DFF (2,5-diformylfuran), which can be obtained by selective oxidation of HMF is more stable and could be easily isolated for direct use or as an intermediate for other molecules or polymers.
Selective oxidation of 5-hydroxymethyl furfural into 2,5-diformylfuran has been described using homogeneous catalysts such as Co/Mn/Br/Zr acetates mixture (Partenheimer W., Gruchin V. V., Adv. Synth. Catal. (2001) 343 (1):102-111) or homogeneous vanadium complexes (Hanson S. K., Wu R., Silks L. A. P. Org. Lett. (2011) 13(8):1908-1911. However, the use of heterogeneous catalysts with O2 is preferred due to its easy separation from the reaction products.
Vanadium oxides V2O5 have then been used in WO9617836A2 publication with a weight ratio of 2 between the catalyst and the 5-HMF. After 1 h 30 of reaction at 170° C. under air at 10 bar in toluene, the conversion is 91% and the yield 62%. By supporting V2O5 on TiO2, keeping the ratio between the catalyst and the 5-HMF at 2, they manage to obtain a quantitative conversion with a yield of 97% in 1 h 30 at 110° C. under air at 16 bar in toluene. However, this type of supported vanadium oxides have been recently studied by Nie and the selectivity toward DFF reported were always below 70% (Nie J., Liu H. Pure Appl. Chem. (2012) 84(3):765-777).
Flow chemical oxidation was performed using supported 5% w/w Pt/SiO2 but only yielded to 60% 5-HMF conversion and 70% selectivity toward DFF at 100° C. under 150 psi of air (Lilga M. A., Hallen R. T., Gray M. Top. Catal. (2010) 53: 1264-1269).
The best selectivity was reported with the use of ICaT-4 15% w/w silver substituted calcined manganese mesoporous material (catalyst/5-HMF weigh ratio of 1) under 15 bar of air at 165° C. in isopropanol which gave 100% selectivity toward DFF with an HMF conversion of 98% in 4 h. This very high temperature is required to get a full conversion, with a 60% conversion at 135° C.
Several studies have reported catalytic systems capable of selectively oxidizing HMF into DFF and in particular the family of vanadium phosphates.
Vanadium oxides and Vanadium phosphates oxides were reported by WO03024947A2 publication for the oxidation of the 5-HMF directly formed by dehydration of fructose without any purifications. V2O5 used in DMSO at 150° C. under air bubbling leads to 58% yield of DFF after 13 h based on the HMF formed. They screened other vanadium oxides such as VOPO4 or VOHPO4.0.5H2O on the oxidation of commercial 5-HMF in DMSO with air bubbling for 5 h and a weight ratio of 0.5 between the catalyst and the 5-HMF at 150° C. The best results showed complete conversion with more than 80% yield in DFF. The use of DMSO makes the recovery of DFF difficult.
Carlini tried then to use VOPO4.2H2O in a 0.4 weight ratio with 5-HMF under 1 bar of O2 in MIBK at 80° C. After 6 h and 98% conversion of 5-HMF, the selectivity toward DFF was 50% (Carlini C., Patron P., Raspolli Galleti A. M., Sbrana G., Zima V. Appl. Catal. A: Gen. (2005) 289:197-204). The use of the toxic high boiling point solvent dimethyl formamide at 100° C. increased the selectivity at 93% with a decrease in conversion at 56%. The incorporation of iron in the structure of the vanadium catalyst made it possible to decrease the ratio between the catalyst and the 5-HMF to 0.01 keeping a high selectivity at 87% and moderate conversion at 59%.
However, these studies on the family of vanadium phosphates mixed oxides indicate that it is very difficult to obtain high conversions and selectivity into DFF and typically high loading of catalysts or high temperatures are required. The vanadium phosphate mixed oxide catalysts have been then demonstrated to be active in the reaction transforming HMF into DFF with limited conversion and selectivity. In the objective of developing an industrialisable process there is a need to uncover new catalysts that can be more active and selective.